The invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a photo mask.
In fabrication of semiconductor devices, a photo mask on which patterns have been formed is used to form the patterns on a semiconductor substrate. The patterns formed on the photo mask are transferred onto the semiconductor substrate by a photolithography process. Thus, the quality of the photo mask is important.
To fabricate the photo mask, a light blocking layer and a resist layer are formed on a transparent substrate. Desired patterns are transferred onto the resist layer using an exposure apparatus. A development process using a developer is performed to form resist patterns. The light blocking layer is etched using the resist patterns as an etch mask to form light blocking patterns. Then, the resist patterns are removed.
Some of the resist patterns may have line widths larger than a desired critical dimension (CD) due to various factors during the process of fabricating the photo mask. The resist patterns are used as the etch mask to etch the light blocking layer. Therefore, if the resist patterns have a large line width, the light blocking patterns also have line widths larger than the desired critical dimension, thus degrading the uniformity of the pattern line width. The uniformity of the pattern line width is an important factor in determining the quality of the photo mask.
Accordingly, many attempts have been made to improve the quality of the photo mask by correcting the resist patterns having the large line width on the photo mask. As one example, after the line widths of the resist patterns formed on the photo mask are measured, the line widths of the respective resist patterns are corrected by adjusting the operating conditions of the exposure apparatus. However, if sizes and shapes of the patterns are changed, the operating conditions of the exposure apparatus must also be changed. Further, it is difficult to control the uniformity of the pattern line width because it is unclear how much uniformity can be improved due to malfunction of the exposure apparatus.